The present invention relates to flexible hinged structures, and particularly to flexible hinged structures which are placed between a pair of substantially rigid panels so that the panels may be hinged one to the other. The panels are formed of a substantially rigid material such as rigid polyvinyl chloride, and the hinge is formed of a flexible plastics material such as polyvinyl chloride. The hinge is configured, however, so as to be resistant to rips or tears, so that the pair of substantially rigid panels to which the flexible hinge has been sealed may be hingedly moved one with respect of the other with impunity.
A co-pending application Ser. No. 09/789,807, filed Feb. 22, 2001, in the names of the inventors herein, teaches a structure which may be fitted to the front edges of shelves and the like, and to which a plurality of substantially rigid plastic pockets may be placed so as to provide pricing or other information with respect to items being displayed on the shelves. Typically, such structure is found in retail stores an the like, in association with household articles and other articles of all kinds, where the retailer wishes to provide pricing information, product specifications, etc.
In order to do so, the co-pending application teaches the structure whereby a plurality of like pockets may be fixed to the display structure on the front of the shelf, and the co-pending application notes that the pockets may be hinged one to another, or hinged directly to the display structure.
When the display pockets are hinged one to another, it is necessary that they shall be secured one to another by a flexible hinge which is sealed to each of the substantially rigid pockets or panels. However, at least two further criteria exist.
The first criterium is that the flexible hinge which secures the substantially rigid panels one to the other must not only be flexible, it must be strong and resistant to ripping or tearing. Unfortunately, soft and flexible plastics material is not, in and of itself, sufficiently resistant to ripping or tearing, and thus the use of soft and flexible plastics material as a hinge structure has not been recommended, until development of the present invention.
The other criterium is that, when in their rest position, the two substantially rigid panels to which the flexible hinge has been sealed should be contiguous one to the other, in back face to front face relationship of the one to the other. This requires that the flexible hinge that is between the substantially rigid panels shall have sufficient elastic memory that the panels will assume the contiguous, face-to-face relationship unless they are being held apart by a user who has hingedly moved one panel with respect to the other so as to view the additional information which is on the back face of one panel or the front face of the other panel which were previously hidden from view.
Thus, the need for a tear-resistant but flexible hinge structure arises. In response thereto, the present inventors have unexpectedly discovered that if a flexible plastic sheet material is reshaped over at least a selected portion thereof so as to provide a structure which essentially comprises a plurality of contiguous webs and ribs, or flat portions and raised portions, which are arranged in a staggered relationship, it is extremely difficult to rip or tear the flexible hinge structure beyond the discontinuity in the configuration of the flexible hinge structure. Thus, a rip or tear which has somehow been causexe2x80x94such as by cuttingxe2x80x94in the flexible hinge structure will not propagate along its length or across its width.
To that end, the present invention provides a tear-resistant, flexible hinge structure for placement between a pair of substantially rigid panels, wherein the flexible hinge structure is made from a flexible plastics sheet material having a first softening temperature, a second elastic memory loss temperature, and a third melting temperature. Of course, the second elastic memory loss temperature is higher than the softening temperature and lower than the melting temperature.
The flexible hinge structure is formed under heat and pressure in the flexible sheet material so as to comprise at least three parallel rows of alternating flat and raised portions, in staggered relationship. That configuration is such that each flat portion is contiguous to 2, 3, or 4 raised portions; and each raised portion is contiguous to 2, 3, or 4 flat portions.
The flexible hinge structure has opposed sides which are sealed one to each of the pair of substantially rigid panels.
The present invention is such that each of the alternating flat and raised portions in each row thereof has a width which is substantially equal to the width of all other flat and raised portions of that row.
Also, the length of each of the flat portions of each of the rows of alternating flat and raised portions is substantially equal to the length of all other flat portions; and likewise, the length of each of the raised portions of each of the rows of alternating flat and raised portions is substantially equal to the length of all the other raised portions.
The flat and raised portions of each row thereof are offset by one-half the length of a flat portion of each row, with respect to the flat and raised portions of each adjacent row thereof.
The thickness of each raised portion of the flexible hinge material, when the flexible hinge has been formed, is greater than the thickness of each flat portion of the flexible hinge material.
Typically, the flexible sheet material is polyvinyl chloride.
The plastic sheet material typically has an initial thickness in the range of 0.010 to 0.025 inches.
The width of each row is in the range of 0.050 to 0.075 inches; and the pitch of one flat portion and one raised portion is typically in the range of 0.0115 to 0.250 inches.
The softening temperature at which the sheet plastics material starts to lose its shape memory and starts to become flexible, is in the range of 175xc2x0 F. to 200xc2x0 F.
The full melting temperature at which the sheet plastics material has fully liquidized is in the range of 275xc2x0 F. to 350xc2x0 F.
The elastic loss memory at which the sheet plastics material has fully lost its elastic memory is in the range of 250xc2x0 F. to 270xc2x0 F.
In general, the flexible hinge structure of the present invention has been formed flat, but is re-formed and cooled in a semi-circular configuration crosswise of the flexible hinge structure.
Typically, there are between three and seven rows of alternating flat and raised portions, usually five rows.
Also, the hinge structure is generally sealed to the substantially rigid panels using radio frequency energy, and pressure, to each of the substantially rigid panels.
The present invention provides a method of making a tear-resistant, flexible hinge structure as described above. The method comprises the following steps:
a) a hard, flat metallic platen is provided.
b) a heat resistant, non-conductive barrier sheet is placed on the platen.
c) a metallic conductive die is provided, where the die has at least three parallel rows of alternating projections and intervening depressions therebetween. The rows of alternating projections and intervening depressions are arranged in staggered relationship, whereby each projection is contiguous to 2, 3, or 4 depressions, and each depression is contiguous to 2, 3, or 4 projections.
d) a pressure producing structure is provided over the metallic platen, together with control means for the pressure producing structure to advance the pressure producing structure towards the metallic platen, and to withdraw the pressure producing structure away from the metallic platen.
e) the metallic conductive die is secured to the pressure producing structure.
f) heating means are provided to heat the metallic conductive die to a predetermined temperature when it is in place on the pressure producing structure.
g) a source of radio frequency energy is provided, and it is connected between the metallic conductive die and the metallic platen.
h) at least a strip of flexible plastic sheet material from which the flexible hinge structure is to be formed, is placed on the barrier material.
i) the metallic conductive die is pre-heated to a temperature of 160xc2x0 F. to 200xc2x0 F.
j) the pre-heated metallic conductive die is advanced against the flexible plastics material so as to contact the same with pressure.
k) stop means are provided to assure that the pre-heated metallic conductive die does not advance so far as to contact the barrier material but that it advances to a distance away from the barrier material which is less than the original thickness of the flexible plastics material from which the flexible plastic hinge is being formed.
l) after step (j) has continued for a first predetermined period of time, the source of radio frequency energy is turned on for a second predetermined period of time.
m) after the source of radio frequency energy has been turned off following step (l), the metallic conductive die is permitted to remain in place for a third predetermined period of time.
n) the metallic conductive die is then withdrawn away from the barrier material, and the flexible plastics material, so as to reveal a formed flexible plastic hinge structure having at least three parallel rows of alternating flat and raised portions.
o) the formed flexible hinged structure is allowed to cool.
The source of radio frequency energy typically has a frequency which is in the range of 70 to 130 MHz.
The pressure which is produced by the pressure producing structure is typically in the range of 450 to 750 psi.
The first predetermined period of time is in the range of 5 to 30 seconds, the second predetermined period of time is in the range 2 to to 8 seconds, and the third predetermined period of time is in the range of 1 to 5 seconds.
The method of the present invention may also comprise the following step:
p) heating the formed flexible hinge structure to a temperature of 250xc2x0 F. to 270xc2x0 F., placing the formed flexible hinge structure in a semi-circular configuration crosswise of the flexible hinge structure while maintaining the temperature thereof in the range of 250xc2x0 F. to 270xc2x0 F., for a period of time in the range 20 to to 45 seconds, and then permitting the semi-circular formed configuration of the flexible plastic hinge to cool.
Of course, the present invention is carried out particularly when the plastics sheet material from which the flexible hinge structure has been formed has a thickness in the range of 0.010 to 0.025 inches.
The present invention may further comprise the step of:
q) during the steps (j) through (m) sealing the flexible hinge structure to the pair of substantially rigid panels by pressure and radio frequency energy.
In keeping with the present invention, each of the alternating projections and depressions in each row thereof on the metallic conductive die has a width which is substantially equal to the width of all other projections and depressions in that row.
The length of each of the projections of each of the rows of alternating projections and depressions is substantially equal to the length of all other projections.
The length of each of the depressions of each of the rows of alternating projections and depressions is substantially equal to the length of all other depressions.
The projections and intervening depressions of each row thereof are offset by one-half the length of a projection of each row with respect to the projections and intervening depressions of each adjacent row thereof.
Typically, the conductive metallic die comprises from three to seven contiguous brass strips, each having the alternating projections and intervening depressions formed therein.
The width of each of the contiguous brass strips is in the range of 0.050 to 0.075 inches.
Also, the pitch of one projection and one intervening depression is in the range of 0.115 to 0.250 inches.
The length of each depression which is formed in each brass strip of the metallic conductive die is typically in the range of 100% to 150% of the length of each projection.